Aaron posted the link to this paper via Facebook:
Selection in Europeans on Fatty Acid Desaturases Associated with Dietary Changes
As the authors comment in the discussion:
"Agricultural diets would have led to a higher consumption of grains and other plant-derived foods, relative to huntergatherer populations. Alleles that increase the rate of conversion of SC-PUFAs to LC-PUFAs would therefore have been favored".
Or to rephrase it slightly, from the legend of Fig 6:
"The adoption of an agricultural diet would have increased LA and decreased ARA and EPA consumption, potentially causing a deficiency in LC-PUFAs".
This is something I have thought about, in more general terms, for some time.
At the time of the switch from hunting animals for their fat to growing grains for their starch the paper suggests that there was a population-wide potential deficiency of the longer chain PUFA, arachidonic acid, EPA and DHA.
This applied a selection pressure to the population. Within the population there was a random distribution of the ability to elongate and desaturate linoleic and alpha linolenic acids to their longer chain derivatives.
People who had this ability in generous amounts did well. Those without, didn't.
What happened to those people who were "without" the lucky gene snps to survive well without animal derived lipids? They didn't "develop" the genes, no individual suddenly develops a better gene. Their intrinsic inability means they didn't reproduce as successfully.
Their genes are currently under represented in the gene pool today.
It has always struck me that the process of getting poorly adapted genes out of the gene pool is what we describe as pathology, illness. Trying to patch it up is what we call medicine. Individuals don't adapt. They either do well or badly. The population "adapts" through the illnesses of those whose genes are not appropriate to the new environment.
The adaptation of our species to the novel situation of agriculture is far from complete. On-going adaptation of a species to a new environment is via the suffering of the individuals with genes more appropriate to the previous long term stable environment. The default for a person with on-going pathology might be to step back 10,000 years rather than continuing to assist evolution of the species via personal pathology. A lot of pathology will be needed.
Miki Ben-Dor has a nice post along these lines this on his blog.
Of course the adaptation to sucrose and bulk seed oils has only just begun. LOTS of pathology needed to adapt the species to those two! Juvenile onset type 2 diabetes is what we call the process.